This disclosure relates to circuits and methods for canceling signal dependent capacitance.
A common problem experienced with electronic circuitry is capacitance, as capacitance may degrade or interfere with circuit operation. Capacitance that interferes with circuit operation is sometimes referred to as parasitic capacitance.
In semiconductor devices, for example, the parasitic capacitance associated with circuits (e.g., NMOS transistors, PMOS transistors, diffused resistors, diodes, and junction capacitors) may be a function of voltage, which voltage dependency may result in unwanted distortion of voltage signals (e.g., an output voltage signal of a semiconductor device). For example, a low pass filter constructed of a diffused resistor and a metal-oxide-metal capacitor may have a voltage dependent parasitic junction capacitance associated with the diffused resistor. When a linear voltage signal is applied to the input of the filter, a non-linear current (required to charge the voltage dependent junction capacitor) flows through the resistor, resulting in a distorted voltage signal at the filter output. It will be understood that the foregoing is merely one example of how voltage dependent capacitance can cause voltage distortions in a wide variety of analog signal processing circuits. It will be further understood that capacitance may depend on signals other than voltage signals.
Accordingly, what is needed are systems and methods for canceling or reducing signal dependent capacitance.